Japan battled on Monday to prevent a nuclear catastrophe and to care for millions of people without power or water after a massive earthquake and tsunami was feared to have killed more than 10,000 people.

The devastation in Japan could worsen the negative short-term sentiment gripping a vulnerable U.S. stock market. Likely to take the biggest hits are companies exposed to Japan and the nuclear energy sector.

The disaster brought on a flurry of short bets against Japanese stocks on Friday, and that trend could well accelerate on news of deteriorating conditions in Japan over the weekend.

Officials in Japan confirmed three nuclear reactors were at risk of overheating, raising fears of an uncontrolled radiation leak.